linux/arch/arm/include/asm/arch_timer.h

#ifndef __ASMARM_ARCH_TIMER_H
#define __ASMARM_ARCH_TIMER_H

#include <asm/barrier.h>
#include <asm/errno.h>
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/types.h>

#include <clocksource/arm_arch_timer.h>

#ifdef CONFIG_ARM_ARCH_TIMER
int arch_timer_arch_init(void);

/*
 * These register accessors are marked inline so the compiler can
 * nicely work out which register we want, and chuck away the rest of
 * the code. At least it does so with a recent GCC (4.6.3).
 */
static __always_inline
void arch_timer_reg_write(int access, enum arch_timer_reg reg, u32 val)
{
	if (access == ARCH_TIMER_PHYS_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mcr p15, 0, %0, c14, c2, 1" : : "r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mcr p15, 0, %0, c14, c2, 0" : : "r" (val));
			break;
		}
	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mcr p15, 0, %0, c14, c3, 1" : : "r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mcr p15, 0, %0, c14, c3, 0" : : "r" (val));
			break;
		}
	}

	isb();
}

static __always_inline
u32 arch_timer_reg_read(int access, enum arch_timer_reg reg)
{
	u32 val = 0;

	if (access == ARCH_TIMER_PHYS_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mrc p15, 0, %0, c14, c2, 1" : "=r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mrc p15, 0, %0, c14, c2, 0" : "=r" (val));
			break;
		}
	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
		switch (reg) {
		case ARCH_TIMER_REG_CTRL:
			asm volatile("mrc p15, 0, %0, c14, c3, 1" : "=r" (val));
			break;
		case ARCH_TIMER_REG_TVAL:
			asm volatile("mrc p15, 0, %0, c14, c3, 0" : "=r" (val));
			break;
		}
	}

	return val;
}

static inline u32 arch_timer_get_cntfrq(void)
{
	u32 val;
	asm volatile("mrc p15, 0, %0, c14, c0, 0" : "=r" (val));
	return val;
}

static inline u64 arch_counter_get_cntvct(void)
{
	u64 cval;

	isb();
	asm volatile("mrrc p15, 1, %Q0, %R0, c14" : "=r" (cval));
	return cval;
}

static inline void __cpuinit arch_counter_set_user_access(void)
{
	u32 cntkctl;

	asm volatile("mrc p15, 0, %0, c14, c1, 0" : "=r" (cntkctl));

	/* disable user access to everything */
	cntkctl &= ~((3 << 8) | (7 << 0));

	asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl));
}
#endif

#endif